全文获取类型
收费全文 | 9583篇 |
免费 | 334篇 |
国内免费 | 79篇 |
专业分类
测绘学 | 283篇 |
大气科学 | 663篇 |
地球物理 | 2836篇 |
地质学 | 3545篇 |
海洋学 | 517篇 |
天文学 | 1716篇 |
综合类 | 42篇 |
自然地理 | 394篇 |
出版年
2022年 | 74篇 |
2021年 | 135篇 |
2020年 | 128篇 |
2019年 | 116篇 |
2018年 | 378篇 |
2017年 | 357篇 |
2016年 | 519篇 |
2015年 | 337篇 |
2014年 | 444篇 |
2013年 | 614篇 |
2012年 | 491篇 |
2011年 | 433篇 |
2010年 | 428篇 |
2009年 | 491篇 |
2008年 | 372篇 |
2007年 | 309篇 |
2006年 | 334篇 |
2005年 | 255篇 |
2004年 | 254篇 |
2003年 | 235篇 |
2002年 | 169篇 |
2001年 | 159篇 |
2000年 | 165篇 |
1999年 | 132篇 |
1998年 | 162篇 |
1997年 | 157篇 |
1996年 | 119篇 |
1995年 | 116篇 |
1994年 | 113篇 |
1993年 | 103篇 |
1992年 | 80篇 |
1991年 | 83篇 |
1990年 | 83篇 |
1989年 | 73篇 |
1988年 | 76篇 |
1987年 | 78篇 |
1986年 | 94篇 |
1985年 | 83篇 |
1984年 | 76篇 |
1983年 | 85篇 |
1982年 | 86篇 |
1981年 | 71篇 |
1980年 | 69篇 |
1979年 | 63篇 |
1978年 | 63篇 |
1977年 | 60篇 |
1975年 | 58篇 |
1974年 | 49篇 |
1973年 | 64篇 |
1971年 | 51篇 |
排序方式: 共有9996条查询结果,搜索用时 296 毫秒
81.
A. Tárczy-Hornoch 《Pure and Applied Geophysics》1962,52(1):53-58
Zusammenfassung Es werden mit Hilfe der sphärischen Trigonometrie und der Ausgleichsrechnung Methoden angegeben, die die Berechnung der bestanschmiegenden Ebene an eine Anzahl von Geraden mit einem gemeinsamen Punkt ermöglichen.
Summary With the aid of the spherical trigonometry and the adjustment, methods are given to determin the best-fitting plane for a given set of directions through a common point.相似文献
82.
83.
Резюме С помощью принятия простых кинематических предположений и на основании ω—уравнения выла определена конфигурация полос облаков
в полностью окклюдированном циклоне без фронтов. Облачная система определяется полем скрытой теплоты, выделяемой в процессах
конденсации. Полосы облаков теоретически представляют собой в основном листы синусоидальной спирали.
Address: Boční II, Praha 4-Spořilov. 相似文献
Address: Boční II, Praha 4-Spořilov. 相似文献
84.
Lock-release gravity currents with a viscous self-similar regime are simulated by use of the renormalization group(RNG) k - ε model for Reynolds-stress closure. Besides the turbulent regime with initially a slumping phase of a conslant current front speed and later an inviseid self-similar phase of front speed decreasing as t^-1/3(where t is the time measured from release), the viseous self-similar regime is satisfactorily reproduced with front speed decreasing as t^-4/5,consistent with well known experimental observations. 相似文献
85.
The three-dimensional problem of the dynamics of a moored floating object under the action of regular waves is solved numerically as a boundary value problem by use of the finite-infinite element method. The cross-sectional shape of the floating body and the mooring arrangements may all be arbitrary. The mathematical formulations of the problem and procedures of the numerical method are presented in this paper. A corresponding computer program WALOAD has been developed, which is capable of computing wave forces on fixed and floating structures. Numerical computations using this program could give very accurate results, even though rather coarse meshes were used. The program is easy to use and is readily applicable in many practical situations. 相似文献
86.
P. Cobo C. Ranz A. Fernández M. Cuesta D.K. Anthony M. Siguero 《Marine Geophysical Researches》2005,26(2-4):87-95
Vertical resolution is of fundamental importance in sonar exploration and is directly related to the duration of the acoustic
pulse generated by the transducer. The shorter the radiated pulse, the higher the vertical resolution. Many sub-bottom profiling
sonar systems use piezoelectric transducers because they are reversible and well understood. Piezoelectric projectors are
normally resonant transducers, which are intrinsically narrowband. A piezoelectric transducer is usually driven by a tone-burst.
However, it is possible to use Fourier techniques to find a pre-compensated electrical driving function so that the transducer
radiates a prescribed wider band acoustic waveform. This technique can be applied to synthesize zero-phase cosine-magnitude,
Gaussian, and bionic pulses, with a conventional sandwich transducer. Zero-phase cosine-magnitude waveforms provide minimum
length pulses (and therefore maximum resolution) within a prescribed frequency band.The aim of this paper is to illustrate
the synthesis of wideband acoustic pulses using an underwater piezoelectric projector. The conventional acoustic waveform
radiated when a Tonpiltz transducer is transiently excited using a “click” and allows its frequency response function to be
measured. This function is used to design the electrical signal which then drives the transducer so that it radiates the shortest
pulse compatible with its mechanical response. The significant resolution enhancement of the waveform shaping process is illustrated
by its application to a sediment wedge model. 相似文献
87.
Periáñez R 《Marine environmental research》2005,60(1):35-49
The presence and temporal evolution (1990-2001) of (226)Ra in a tidal estuary affected by the phosphate industry has been investigated. Water samples collected in the course of four separate sampling campaigns were analysed for (226)Ra content using a gas flow proportional counter following Ba coprecipitation. Two (226)Ra sources have been identified: direct discharges from the industrial complex and run-off from a phosphogypsum pile. Although activity levels are similar, or even higher, than those found in other environments affected by the phosphate industry, there has been a general decrease in contamination since direct discharges ceased in 1998 due to new regulations from the EU. However, sediments are now acting as a source of Ra to the water column due to redissolution processes. A numerical model of the estuary has been developed to describe quantitatively the experimental results. The model solves the hydrodynamics and the dispersion equation of (226)Ra including interactions with sediments. Model results are, in general, in good agreement with observations. 相似文献
88.
1 .IntroductionTheBohaiGulfisinfestedbyiceinthewholewinter,andoffshorestructuresthereexperiencenotonlywind ,waves ,currentsandearthquake ,butalsoiceloadswhicharecomplicatedbecauseofthedynamicinteractionbetweenicesheetsandstructures.Duanetal.( 2 0 0 0 )hadacomprehensivere viewofthelatestadvancesonice inducedvibration ,fatigueandfractureofoffshorestructures ,payingmuchattentiontothedifferencesinicebreakingmodeanddynamicsofstructuresindifferentice in festedwaters .Theypresentedcriticallythelates… 相似文献
89.
This paper addresses an important problem in ship control application—the robust stabilization of underactuated ships on a linear course with comfort. Specifically, we develop a multivariable controller to stabilize ocean surface ships without a sway actuator on a linear course and to reduce roll and pitch simultaneously. The controller adapts to unknown parameters of the ship and constant environmental disturbances induced by wave, ocean current and wind. It is also robust to time-varying environmental disturbances, time-varying change in ship parameters and other motions of the ship such as surge and heave. The roll and pitch can be made arbitrarily small while the heading angle and sway are kept to be in reasonably small bounds. The controller development is based on Lyapunov’s direct method and backstepping technique. A Lipschitz continuous projection algorithm is used to update the estimate of the unknown parameters to avoid the parameters’ drift due to time-varying environmental disturbances. Simulations on a full-scale catamaran illustrate the effectiveness of our proposed controller. 相似文献
90.